The Nikon eReview: NSR-S610C Immersion Scanners Meet Production Requirements for 45 nm and Beyond

When immersion lithography was first introduced, the key obstacles that had to be overcome for mainstream production were defectivity, overlay performance, aberration stability, and throughput. Today, Nikon NSR-S610C immersion scanners (NA = 1.30) are being used in high-volume manufacturing in leading-edge facilities around the world. These systems are processing more than 2000 wafers per day while delivering low defectivity levels, with overlay and aberration performance meeting all production requirements for 45 nm applications and beyond.

Figure 1. The Nikon nozzle performs with no tool-induced immersion defects, is fully compatible with a wide range of receding contact angles, and has no restriction on advancing contact angle.

Although defectivity was initially considered a major manufacturing risk for immersion technology, Nikon immersion scanners consistently deliver defectivity performance on par with today’s most advanced dry ArF systems (Figure 1). Process flexibility is an essential factor in the high-volume production environment, and the Nikon nozzle is compatible with a wide range of materials with differing receding contact angles (RCA) and has no restriction on advancing contact angle (ACA). Nikon also continues development efforts to further enhance the nozzle design in preparation for future tools and double patterning.

The potential for system contamination as a result of the introduction of water within the scanner was another manufacturing concern. Fortunately, the Nikon design requires no regular system cleaning. In the case of a fab excursion such as an accident in resist coating, topcoat peeling due to a process issue, or particles brought in by a dirty wafer, Nikon has developed an effective tool cleaning method to resolve such issues (Figure 2).

Figure 2. Although regular system cleaning is not necessary, the S610C enables effective tool cleaning in the event of a fab excursion.

Initially, overlay accuracy and system stability were concerns for manufacturing. The Nikon Tandem Stage design minimizes wafer processing variability by exposing wafers only on the single Exposure Stage. This eliminates stage mismatching errors and optimizes accuracy. The S610C has already demonstrated overlay accuracy (|M|+ 3σ) x = 4.2, y= 2.9 nm performance, close to satisfying double patterning requirements of x and y = 2.9 nm. Overlay stability is equally critical in the manufacturing environment, and the S610C avoids temperature fluctuations that impact stability by utilizing a continuous water flow and surface tension to manage water containment. Combined with frequent system checks using the Calibration Stage – the S610C delivers overlay accuracy and stability that easily meet production requirements beyond 45 nm (Figure 3).

Figure 3. The S610C delivers overlay stability |M|+ 3σ < 5.0 nm across multiple lots.

Although immersion technology enhances imaging capabilities, lens aberrations were potentially problematic. The S610C lens design minimizes the image distance from the lens axis to provide optimal thermal and field aberration control. However, within the production environment, aggressive off-axis illumination techniques increase the risk of RET-induced thermal aberrations. The Nikon Infrared Aberration Control (IAC) system significantly reduces such aberrations by using an infrared laser and optical fibers to selectively heat the lens pupil to correct for uniform astigmatism caused by dipole-like illumination conditions (Figure 4).

Figure 4. The Nikon Infrared Aberration Control system selectively heats the lens pupil to correct for uniform astigmatism caused by dipole-like illumination conditions.

As double patterning (DP) is integrated into manufacturing, CD uniformity also becomes increasingly important. In the case of Line DP, the CD errors between the two exposures will impact the total CD variation, driving more aggressive CDU requirements for each separate exposure. The Tandem Stage enables frequent focus and illumination calibrations to enhance CD uniformity and stability. The S610C meets the DP space CDU requirement of 3.3 nm (3σ) as defined by the ITRS roadmap for 32 nm (Figure 5).

Figure 5. The S610C already meets the aggressive CDU requirements for double patterning applications.

The last potential manufacturing roadblock for immersion integration was system productivity and throughput. As noted above, Nikon immersion scanners do not require any regular system cleaning – eliminating that productivity detractor. In addition, the Tandem Stage design enables continuous wafer processing for maximized throughput. Today, Nikon S610C scanners are running in leading-edge manufacturing facilities worldwide, processing more than 2000 wafers per day, with excellent uptime (Figure 6). Although immersion lithography presented many challenges for manufacturing integration, the Nikon NSR-S610C clearly satisfies all requirements for 45 nm high-volume applications and beyond.

Figure 6. S610C systems are delivering average uptime > 96% and processing more than 2000 wafers per day.